Conventional rotary extrusion blow molding apparatuses typically have a structural frame mounted on a rotating shaft. The structural frame has a plurality of molds mounted thereon and is known in the industry as a wheel. As the wheel is rotated, the plurality of molds is rotated past an extrusion die extruding a continuous parison. Each mold typically includes two mold halves, each comprising a mold cavity half therein, such that when the mold halves are closed, the mold defines a mold cavity corresponding to the configuration of the article to be molded, such as a container. Each mold, seriatim, is rotated past the extrusion die with the mold halves in an open configuration. The mold halves of each mold are then closed around the parison to enclose the parison within the mold defined by the mold halves. A blowing needle is then inserted into the parison within the closed mold and internal pressure is introduced to the parison, forcing it to inflate and conform to the configuration of the mold cavity. The molded object is then cooled and the mold opened to release the molded object from the mold.
As the wheel is rotated, cam followers positioned on each mold engage a cam track. The cam followers follow the cam track, causing the cam followers to move laterally relative to the rotational movement of the wheel. The lateral movement of the cam followers controls the position of the mold halves and their movement between the open and closed positions.
When the two mold halves are clamped over one or more parisons prior to blowing of the parisons to form plastic containers, high clamp forces are required to close the mold halves on the parisons to pinch off the plastic and to hold the mold halves closed during blow molding. As some of the high clamp forces are transmitted through the cam followers, the cam track must be made of substantial material to withstand the forces applied to the walls thereof. This is particularly important in transition areas of the cam track. The continuous motion of the rotary molding apparatuses intensifies the wear issues, and therefore, the cam track must be made to withstand the high wear forces associated therewith. Additionally, in order to provide the precise control needed to provide quality molded products, the positioning, dimensioning and configuration of the cam track must be precisely controlled in order to provide the precision necessary for the opening and closing of the mold halves.
Due to the above-recited requirements, the cam tracks are generally made in one piece to provide the strength and dimensions required. However, due to the relatively large size of the cam tracks (generally 50-60 inch radius), these cam tracks are difficult and costly to manufacture and ship. In addition, when adjustments or maintenance is required on the cam tracks, the blow molding apparatus must generally be taken out of operation for a significant period of time while the adjustments or maintenance are performed.
Accordingly, there is a need for an improved molding apparatus and cam track which is easy and cost-effective to manufacture and which allows for ease and efficiency of adjustment and maintenance.